To Change theme of Default page

I'm not sure I understand the question. The theme for the site covers the home page as well as the other pages of the blog. You can change themes via the admin area of the website.

If you find a theme that you want to use, but desire to change aspects of how the home page looks, then make a copy of that theme's folder, giving it a new name, switch to your new theme in the admin area, and then changes the style.css file of that new
theme to suite your needs.

Sorry, my bad. What I should have written is that I want one style for the pages and another style for the posts. Using the Standard theme, the pages will not display the side panel (Category List, Tag Cloud, etc.) but the posts will.

Pretty much same code as above, only instead of ServingLocation.SinglePost check for ServingLocation.SinglePage. In that second css file, override styles you need for page to look different and you done.